278 THE VOYAGE OF H.M.S. CHALLENGER. 
arms, however, for they bear the pinnules as their larger fellows do; and in some forms 
the lowest of them (tertiary arms) have a series of unequal axillaries and bear armlets on 
their inner faces just as the large outer arms do. In such individuals these ner tertiary 
arms are more equal in size to the outer pair. The two extreme types are well represented 
on Tab. 97 of the Encriniden, figs. 5 and 6, by Quenstedt, who partially founds upon 
them the distinction between the “ Briariden” and the ‘“‘Subangularen.” In the former 
group the inner tertiary arms are undivided armlets like those which come off farther out 
on the ray; while the inner tertiary arms of the Subangularen, though smaller than the 
outer ones, bear armlets on their inner faces, which correspond to those on the inner faces 
of the outer arms that spring from the same axillaries. 
Owing to the presence of these armlets on the inner tertiary arms, the Subangularen 
generally have the “ finger-reichsten Krone” as pointed out by Quenstedt. This is not 
always the case, however, for in a specimen from the Posidonia-beds of Holzmaden, which 
is figured by him,’ the inner tertiary arms are undivided, and their successors are more 
equal to the outer arms of the ray than in some forms of Extracrinus briareus. 
Under the name of Pentacrinus briareus minutus, Quenstedt? has figured a curious 
little species in which the division of the arms seems to be somewhat irregular, and the 
distinction of arms and armlets less marked than is usually apparent in Hetracrinus. 
But I do not think that this variation, even if it be established, need have much effect 
upon the stability of Kxtracrinus as a generic type. 
The differences between the Liassic and the recent Pentacrinide on which the genus 
was founded by the Messrs. Austin were at first regarded by the late Sir Wyville 
Thomson as of merely subgeneric value. Believing that Pentacrinus briareus “seems to 
have a just claim to be recognised as the type of the genus Pentacrinus,” he introduced 
the name Cenocrinus for the Pentacrinus caput-Meduse of Miiller, and one or two fossils 
which closely resemble it.? He subsequently abandoned this name, however, and referred 
the type to Pentacrinus as all later writers have done, some recognising Hatracrinus as 
a separate genus and some not. The Messrs. Austin* pointed out that Miller “in his 
arrangement of the Crinoidea has taken the Pentacrinus caput-Meduse for the typical 
species, while at the same time his generic plate represents the dissected skeleton of quite 
a different Crinoid. In the hope to remedy this intermingling of genera, we propose to 
retain Miller’s genus Pentacrinus, and to continue the Pentacrinus caput-Meduse as the 
type of the genus;” while the name Hxtracrinus was proposed for the Liassie Pentacrinus 
briareus and Pentacrinus subangularis. This arrangement seems decidedly preferable 
to that proposed by Sir Wyville, who eventually gave up Cenocrinus as a subgenus ; 
though I cannot learn that he ever formally adopted Hxtracrinus. 
A second subgenus of Pentacrinus besides Cenocrinus was also proposed by Sir 
1 Eneriniden, Tab. 101, fig. 1. 2 Thid., Tab. 99, fig. 177. 
3 Sea Lilies, The Intellectual Observer, August 1864, p. 3. * Monograph, p. 
